1. Field of the Invention
The present invention relates to a waveform display device for displaying a vibration period of a machine tool by converting the same into a length on a machined surface.
2. Description of the Related Art
To improve the quality of a product machined by a machine tool, analyzing waveform data is important for specifying a cause of machining unevenness (such as a stripe pattern) that has been generated on a machined surface of the product.
For example, waveform data that has been measured and data, such as position information of a drive shaft and a tool tip end point are analyzed so that specifying a vibration source that is a cause of machining unevenness is performed. Examples of such a vibration source include vibration of a drive shaft of a machine tool, an oil pump for cooling, and a fan of a strong current board of a machine tool. In general, each vibration source has an inherent vibration frequency (i.e., a reciprocal of a vibration period), and measurement results of a vibration frequency inherent in a vibration source and a vibration frequency of machining unevenness that has been generated on a machined surface of a product are compared with each other to specify the vibration source that is a cause of the vibration frequency.
FIG. 19A is a diagram schematically illustrating an example of machining unevenness that is generated on a machined surface of a product and illustrating a relationship between a direction of machining by a tool of a machine tool and machining unevenness. FIG. 19B is a diagram schematically illustrating an example of machining unevenness that is generated on a machined surface of a product and illustrating an example of measuring a vibration frequency using a scale. As illustrated in FIG. 19A, on the machined surface, machining unevenness (stripe pattern) having a certain period (i.e., a certain frequency) is generated due to some vibration source along a direction of machining by a tool of a machine tool. As illustrated in FIG. 19B, an interval of a stripe pattern is measured using a scale (ruler). For example, when 27 pieces of stripes are generated in a section of 20 mm measured by the scale, an interval of the stripes is 0.741 mm. When a feeding speed of the tool of the machine tool is 2000 mm/min, a vibration frequency is 45 Hz (=2000/60/0.741).
Analysis of waveform data can be made also by comparison of distance bases on a machined surface on which machining unevenness (stripe pattern) exists other than by comparison using the frequency basis as described above.
For example, as disclosed in Japanese Patent Publication No. 5302371, there is an invention in which time series data, such as speed of a drive shaft and a tool tip end point, is converted into distance-based physical data of a horizontal axis movement distance.
The invention as disclosed in Japanese Patent Publication No. 5302371 is useful when the same machining program is performed while machining conditions, such as a machining speed, are changed, and physical data of a horizontal axis time is converted into distance-based physical data of a horizontal axis movement distance, thereby comparing physical data at the same machining position under different machining conditions (such as speed).
Position information of the drive shaft of a machine tool is time-based information that is acquired by a position detector at every moment. Such a time-based waveform cannot be compared directly with machining unevenness (stripe pattern) actually generated on the machined surface, which needs some processing for finding correspondence between the time-based waveform and distance data on the machined surface, and operations are complicated.
In addition, for example, the invention as disclosed in Japanese Patent Publication No. 5302371 fails to calculate a movement distance in a designated time section, and accordingly fails to analyze waveform data by finding correspondence with an interval of a vibration frequency of the machined surface. Further, frequency characteristics fail to be displayed on a distance basis.